This apparatus was photographed at the University of
Colorado physics department in 1975.

The placard says that it is a Piezoelectric Source,
and that it works by applying a known force supplied by a hanging weight to
a calibrated quartz crystal. The design is by Pierre Curie (1859-1906).

The piezoelectric effect was discovered by Haüy,
who found that a crystal of calcspar squeezed between the fingers became
electrified. There are inverse effects: squeezing a piezoelectric crystal
produces a potential difference, while applying a potential difference causes
a deformation of the crystal.